On paper, Anglo-Jewish organisations are estimated to raise £500m a year through donations and legacies (although the figure is misleading because some of the money transferred from trusts to service providers is counted twice). But with a growing proportion of elderly people in the non-Charedi community and an expanding educational infrastructure to support, the charity budget looks unlikely to shrink.
On top of that, demographic trends in the Jewish community could make it harder for charities to reel in the funds - a challenge highlighted by a report published last week by the Institute for Jewish Policy Research.
According to JPR, older Jews give more than younger Jews, especially to Jewish causes; and religious Jews and synagogue members give more than secular and unaffiliated Jews.
Since the under-30s are more religiously diverse than their elders with a higher proportion of both Charedi and secular Jews, this suggests a future contraction in the donor pool for mainstream Jewish charities.
If secular Jews are more inclined to support non-Jewish than Jewish causes and their numbers grow, there will be fewer potential contributors to Jewish charities unless those charities can find new ways to appeal to them.
Charedim, meanwhile, although they are the most generous charity-givers, are also less well off than other Jewish streams, with less income overall to give away.
If Jewish charities are to keep the money flowing in, they are going to have to redouble efforts to reach those now in their 30s and 40s.
"The generation above felt their responsibility was to the Jewish community first," says Mr Johnson. " I do not think that this is so widespread among my generation and the generation below.
"We need to be able to broaden our funding base. We have to be able to encourage those who are in a position to be philanthropic to focus more of their resource on the Jewish community and inculcate a broader notion of communal responsibility."
But charities also may need to adapt their fundraising to attract them, he suggested. While the younger breed of donor may be ready to part with their cash, they may be more demanding before they do so.
"They view it more as a business proposition," he says. "The charity has to identify the need, the cost and make its case. They are less willing simply to hand over a cheque and say 'I'm willing to trust you to spend my money'."
Finding new donors does not mean cultivating only the select few capable of making five or six-figure contributions. Former World Jewish Relief fundraiser Paul Stein, who now works in the general sector, believes that "mid-value" givers able to donate £500 to £2,000 a year represent "a massive untapped market".
The Jewish sector, he says, is "teeming with these prospects". But they may need a more personal approach to gain their allegiance rather than emotive mailshots and standard newsletters, he argued.
Kate Goldberg, chief executive of one of the major Jewish trusts, the Maurice Wohl Charitable Foundation, argues that investing in "high-quality" Jewish education would help create the donors of the future.
For Mr Stein, securing more legacies is "absolutely vital". Legacy income should ultimately match that from appeal dinners, he argues.
In particular, the babyboomer generation - "the wealthiest generation" ever, the JPR report stresses - could prove a rich source of legacy pickings as it approaches retirement.
Another possibility is for charities to make their income go further by reducing overheads. Instead of each organisation running its own administration, it could cut costs by working with others.
"The answer has to be collaboration," Mrs Goldberg says. Working with the Charedi community on joint services and initiatives could be vital.
